Two way mirror is a mirror that is reflective on one side but is a see through on the other side, such as those that seen in the Hollywood detective movies. People from one side can see only their image while those from the other side can see those from the opposite side. It is commonly used in police stations or psychiatric institutions. However, people are worried they are used in some areas such as dressing rooms, work places or hotels. Here is how to know if the mirror is two way or not at Wiki How to.